Dobson Unit
D1. Physical and chemical oceanography and marine meteorologyDefinition
Unit measuring the thickness of the ozone layer.
The Dobson unit (DU) is the standard measure of total-column trace gas, used mainly for atmospheric ozone, where one DU is the thickness in hundredths of a millimeter that the gas would form if compressed to 0 degrees C and 1 atmosphere. One DU equals 2.69 x 10^16 molecules per square centimeter. Global mean column ozone is near 300 DU, a layer about 3 mm thick at surface conditions; the Antarctic ozone hole is defined below 220 DU. It enters ocean science through satellite ocean-color and UV-penetration work, since stratospheric ozone sets the surface ultraviolet flux that drives photochemistry and affects phytoplankton.
Source: NASA Ozone Watch; WMO/GAW ozone monitoring